Another 47 are missing, presumed drowned. All those on board were from Morocco and Tunisia.
The news came as a row erupted over Italy's decision to send migrants back to their point of departure.
Three planeloads of migrants were flown to Libya on Saturday, and a further 800 people are due to be expelled.
The Tunisian navy says the immigrants' boat sank only an hour after it had set off for Italy.
Eleven people were rescued and the search for possible survivors is continuing.
"It's another regrettable example of the tragedy of irregular migration from sub-Saharan Africa and north Africa to the northern shores of the Mediterranean in Europe," a spokesman for the International Organisation of Migration told AFP news agency.

Entry point
In an abrupt change of policy, the Italian government decided at the weekend to send three planeloads of migrants from Africa, Asia and the Middle East on the small island of Lampedusa back to Libya.
Hundreds of migrants have arrived on the island in the past few weeks, the nearest geographical point of arrival in the European Union from north Africa.
Refugee groups have expressed concern that the migrants have been denied access to proper asylum procedures.
The director of the Italian Council for Refugees, Christopher Heine, told the BBC that many of the migrants came from countries such as Sudan, with severe conflicts and human rights violations.
"Not giving these persons the possibility to claim asylum in a European country is totally contrary to all the rules and regulations and international conventions, starting with the 1951 Geneva Convention, to which, of course, Italy is bound," he said. The United Nations' refugee agency says it has written to the Italian and Libyan governments, requesting access to the migrants. "We would request that everyone gets a chance to be assessed to see who needs protection and who does not," a spokeswoman told BBC News Online.

Abuse fears
Those who survive the dangerous journey to the tiny island of Lampedusa used to be taken to reception centres on Italy's mainland.
"Sending back illegal immigrants by plane is a method we'll increasingly use. It is useful to discourage the departure of illegal immigrants to Italy," Interior Undersecretary Alfredo Mantovano said in an interview with La Stampa. "If they know they will be sent back, maybe they won't leave." Libya is not a signatory to the UN's Geneva Convention on refugees and has been accused of widespread abuse of migrants.
It is unclear what will happen to those refugees, although the UNHCR says it believes they are still in Libya.
The BBC's Rana Jawad in Tripoli says the migrants will be held in detention centres before being flown back to their country of origin.
The Italian authorities believe many migrants sail from Libya in small boats run by people smugglers. Italy has promised to give Libya equipment to detect and halt the boats, with training also pledged.
At least 1,200 people are currently in the island's only reception centre, designed to hold up to 200 people.
A spokesman for Medecins Sans Frontieres, which treats migrants as they arrive in Lampedusa, told the BBC that conditions inside the centre would be extremely difficult.